The present invention relates to a closing device for a coke oven typically encountered in so-called “Non-recovery” or “Heat-recovery” coke oven batteries. The present invention also relates to a method for operating such coke ovens with the inventive closing device. The closing device closes horizontally directed openings of coke oven batteries in a manner that is as impermeable to air as possible. These openings situated at the front and rear side oven walls serve for charging horizontal coke oven chambers which are cyclically operated and which are pushed and charged, respectively, upon completion of a coal carbonization cycle.
Some types of coke ovens are also charged through openings located in the oven top area. The openings positioned at the lateral oven walls then serve to level-off the coke cake with levelling devices, e.g. leveller bars. Thereby, charging cones frequently occurring on charging and adversely affecting the coal carbonization process can be leveled off and the bulk density of the coke cake can be optimally adjusted for the coal carbonization process by leveling facilities.
Frequently the oven doors are integrated into oven walls and embraced by them. Depending on the size of openings or doors, they can seal-off the entire lower area of an oven or cover only parts in order to achieve an optimal charging and homogenization of the coke cake. The coal carbonization process takes 16 to 192 hrs for one coking cycle, depending on the implemented plant design, and it is carried out at temperatures ranging from 800 to 1500° C. At the corners of a coke oven, the temperature is a little lower than in the center.
Owing to the cornered shape of a coke oven, it has recesses and inaccessible spots which adversely affect the coal carbonization process because due to thermal conduction towards the outside, coke, and especially coke in the corners, is noticeably cooler than the main coke cake in the interior. Owing to their design and construction with joints and gaps in the brickwork, the corners and edges of a coke oven, in particular, have an increased thermal conductivity towards the exterior. Moreover, there are load-bearing devices installed in the area near the door which do not contribute to heating-up. Secondary air soles frequently do not reach to the door underside so that this area is noticeably cooler.
Walls of coke ovens are frequently made of refractory bricks. Typical materials for the design and construction of walls are masonry bricks or other suitable refractory construction materials. These substances have a high resistance to heat from the coal carbonization process and dissipate only a small part of the heat occurring on coal carbonization to the exterior so that heating from foreign sources is usually not necessary. The heating of coke ovens is realized by supplying air into the oven chamber with a partial combustion of the coal charged. For this purpose, a precisely dosed quantity of air is supplied. On charging a coke oven, coal is usually not filled up to the oven top but only up to part of the height of the entire oven.
The oven free space located there above is utilized for capturing gases which evolve during a coal carbonization process. A partial combustion of substances dissipated by coal takes place in the oven free space when heated-up. To this effect, a sub-stoichiometrical quantity of air required for combustion, the so-called primary air, is fed in. The openings for primary air feeding are so laid that air streams into the oven free space above the coke cake. This is realized through openings in the area of the oven wall above the oven door or through openings in the oven top area.
Partially burnt gases evolving during the combustion process are collected and passed through channels within the coke cake, wall or doors into the area under the oven floor. These channels are also called “downcomer” channels. So-called secondary air soles formed by channels extending under the oven floor and in which gases from coal carbonization are burnt with additionally supplied air, the so-called secondary air, are located in the area under the oven floor. Since the floor of a coke oven usually has high thermal conductivity, the coal carbonization process is also heated from below by this secondary combustion.
“Downcomer” channels may rest in form of metal tubes in the coke cake, but they can also be accommodated in walls located away from the doors. Thereby, the oven free space is relieved from the pressure building-up during the coal carbonization process. Finally, coking gases can also be discharged trough intermediate spaces in the doors. Thereby, coke oven doors are relieved from the pressure building-up there.
Doors in the coke oven chamber wall on the front side of a coke oven are frequently designed and built as door frames with a base plate. So-called plugs comprised of a material highly resistant to heat and sealing the coke cake on coal carbonization beyond the wall thickness versus the environment are mounted on them. During a coal carbonization process, such doors can keep heat losses towards the exterior at a relatively low level, if the door plug tightly seals the space between coke oven chamber and coke oven door. A heat loss during pushing of a coke oven chamber only occurs if cold air reaches into the interior of a coke oven chamber and if a heat loss can be realized by radiation.
Doors of coke ovens can be fabricated both from metals and refractory oven construction materials. Frequently oven doors are made of a ceramic material, because doors made of metal have some drawbacks. A major problem of metallic protection shields is thermal expansion. A consequence of thermal expansion versus the ceramic material of the embracing wall is that the door may deform during the coal carbonization process and fails to fit exactly on the opening, whereby false air can be aspirated.
Another problem of metallic doors is permanent deformation. Depending on the steel used, a severe inward or outward bulging will occur. If exposed to extreme thermal loads, all steel grades evidence permanent deformation. Moreover, the production of steel highly resistant to heat is expensive and its processing is difficult. Another problem is posed by the high level of surface radiation of metallic oven doors which results from the high thermal conductivity of this material.
Doors which are exclusively built-up of refractory construction materials, in turn, have a disadvantage in that they are heavy in weight and require stable door bodies as well as actuating devices. Refractory bodies are frequently implemented in form of so-called plugs into a door body frame. These refractory door plugs often fail to provide sufficient tightness, thus allowing coking gases to escape to the exterior and carbon to penetrate into the connecting elements between door and ceramic body. As a result, the door may suffer from damage which frequently entails extensive repairs and premature replacement of doors. Frequently located between door frames and plugs are gas collecting spaces which are mixed with fine dusts and carbon due to leakages in ceramic bodies. Moreover, this ceramic structure of material often leads to fractures in the plug, necessitating costly door repairs.
DE 2945017 A1 describes a coke oven door made of a metallic material. The metallic material is framed in form of a plug in a door moving device. The plug is so constructed that it forms a vertical gas collecting space in its interior extending in longitudinal direction and being accessible to gaseous coking products. On the side facing the oven chamber, the plug is comprised of openings through which gases can be passed into the collecting space and to combustion or further processing. To achieve better thermal insulation, an insulating device comprised of a thermally insulating material can be mounted between door and plug. The plugs can be comprised of multiple parts or be provided with expansion joints to compensate for thermal expansion. The actual door plug can be connected by bolting devices to the door body. The coke oven door covers the entire coke oven chamber wall on the front side of an oven. Through special openings, a connection is established between the door-side vertical and chamber-side horizontal gas collecting spaces.
EP 186774 B1 describes a door plug made of a ceramic material. The door plug is bolted or wedged with a metal carrier frame. In outward direction from the door plug, there is an insulating layer which together with the door plug forms a gas collecting space. Thereby, the door seals are relieved as gas is discharged to the gas collecting space and ultimately into the secondary air sole. In operating status, the plugs protrude into the oven chamber and keep the oven charge at a certain distance away from the door body, with the door body being pressed by a latching device against the door frame of the oven during the carbonization process. In particular, a hydraulically bonding refractory concrete is provided for as ceramic material. Essential constituents of refractory concrete are aluminum oxide, silicon oxide and iron oxide. The ceramic plate can also be comprised of exchangeable elements. This allows for easier exchange in case of damage. Except for some small recesses, the coke oven door covers the entire coke oven chamber wall on the front side of the oven.
All door designs and structures available have a disadvantage in that they can be easily damaged because they are exposed to high mechanical forces during opening and closing. Doors made of a ceramic material can be easily damaged and on the whole they have a shorter service life. Conversely, door plugs made of a metallic material are exposed to loads due to thermal expansion whereby they may be deformed and consequently they cannot seal the oven door tightly after a short time. Moreover, owing to thermal expansion, the doors may get stuck in closed position which implies a safety risk for a coke oven with a high heat throughput.
Doors of coke oven chambers must tightly close the coke oven chamber above all during the coal carbonization process. By-products that may escape from a coke oven chamber through leaky coke oven doors are produced during coal carbonization. In particular, these are coking gases and tarry condensates. They pose some risk and hazard to environment and operating staff. Moreover, on coke pushing, cold air penetrates trough a door opening into a coke oven and causes a coke oven chamber to cool-off. This is disadvantageous because combustion of coke oven gas frequently just is sufficient to generate the coking energy. Consequently, a cooling-off of coke oven chamber walls entails increased coal consumption and deterioration in coke quality.
Now, therefore, it is the object of the present invention to provide a door design and structure for a coke oven battery or for an oven bank that evidences no problems with high temperature differences on pushing of coke oven chambers. It should be designed to tightly seal the oven interior, thus preventing any fine constituents from escaping from the oven chamber to the exterior which might pose difficulties to operating the coke oven chamber and which represent a hazard to environment and a problem to coke oven operation. While pushing the contents out from a coke oven chamber, as little cold air as possible should enter into the interior of a coke oven chamber, keeping the heat loss due to radiation to the exterior as low as possible.
The material of the door structure should be stable to temperature impacts and be fracture-proof, thus affording high service life and involving low cost of operation. Finally, the material should be cheap in production. Another object of the present invention is eliminating irregularities in temperature distribution of the coke cake resulting from the cornered shape of the coke oven chamber. A deteriorated coal carbonization in the cooler corners of the coke oven battery should be prevented, if possible.